1 May 2011

Jennie Brand-Miller on why gestational diabetes numbers will double‘Apart from re-living ‘The Sound of Music’ at the 6th International Symposium on Diabetes in Pregnancy meeting in warm and sunny Salzburg, I learned that the findings of the HAPO Study (Hyperglycemia and Pregnancy Outcomes Study) are changing the way the world diagnoses gestational diabetes (GDM, or diabetes first recognised during pregnancy). One of the following is now sufficient:

Fasting glucose: above 5.1 mmol/L

1 hour post 75 gram of glucose: above 10 mmol/L

2 hour post 75 gram of glucose above 8.5 mmol/L

These new guidelines have been accepted by many developed nations and are now in the process of being officially adopted. Using these guidelines will automatically mean that the rate of GDM will increase dramatically. For example, in Australia, this means that about 16% of pregnant women (up from around 8%) will now have a diagnosis of GDM, that’s 1 for every 6 pregnant women. In some ethnic groups, such as South Asian or Chinese women, it will mean 25–30% of women (1 in 3 or 4).

Why have they moved the goal posts? Well, HAPO was one of the biggest studies every done in pregnant women (over 25,000 women from 15 centres in 9 countries). They enrolled only healthy women, specifically excluding those already diagnosed with gestational diabetes according to the old guidelines. The aim was to see if women whose blood glucose levels were ‘intermediate’, that is, high but not so high as to be classed as GDM, were also at risk of having adverse outcomes (e.g. having an emergency caesarean section).

What they found surprised many. There was a very strong link between higher glucose levels and the rate of caesarean section (planned or unplanned), the rate of shoulder dystocia (where the baby’s shoulder is too large for the birth canal) and the chance of having a very large baby, with a weight higher than the 90th percentile. In other words, these women with intermediate BGLs were in need of just as much care as women with diagnosed diabetes, yet as no one thought there was a problem, they were not receiving it.

Another reason why the findings of HAPO were so important relates to what’s called ‘metabolic programming’ and the current epidemic of child obesity. In Australia, like other nations, birth weights have been steadily increasing, and 1 in 5 children is now classified as overweight or obese by only 2–3 years of age. We already know that birth weight correlates with the mother’s BGLs. So, the best way to reduce birth weight, and therefore the likely risk of an overweight child, is to focus on the mother’s BGLs. Ongoing research will determine whether a low GI diet in pregnancy reduces the risk of having GDM or an overweight baby. Stay tuned …’